As a result, hay is the leading crop in Wyoming in terms of value of production.

More than half of the irrigated land in the state is in a hay crop — primarily alfalfa — but there are many acres in perennial cool-season grass such as smooth bromegrass.

If managed properly, perennial cool-season grasses can annually produce two to three tons or more hay per acre.

Proper management includes nitrogen fertilization, but it has become expensive.

If there are grasses that use nutrients more efficiently, especially with respect to nitrogen, and produce more forage on less fertilizer, hay producers could possibly lower fertilizer costs without sacrificing hay yields or stand longevity.

Hay Yields by Nitrogen Rate

A research project funded by a USDA Western Sustainable Agricultural Research and Education grant was conducted at the Gerry Miller ranch near Buffalo in 2010 and 2011 to compare hay yields of the following eight cool-season perennial grasses under flood irrigation fertilized with nitrogen:

1. Paiute orchardgrass

2. Paddock meadow bromegrass

3. Manchar smooth bromegrass

4. Luna pubescent wheatgrass

5. Oahe intermediate wheatgrass

6. NewHy hybrid wheatgrass

7. Hycrest crested wheatgrass

8. Bozoisky russian wildrye

The grasses were seeded in April 2008 and were in their second and third years of production.

Nitrogen rates ranged from 0 to 250 pounds per acre of actual nitrogen applied in late April.

The grasses were harvested on June 22, 2010, and on July 2, 2011.

Actual hay yields of each grass by nitrogen rate for the two years were analyzed to develop nitrogen response curves.

Statistical analyses response curves show what the potential hay yields of each grass would be at any level of nitrogen between 0 and 250 pounds per acre.

The R2 values for each equation ranged from a low of 0.32 for Bozoisky Russian wildrye to a high of 0.87 for Luna pubescent wheatgrass.

An R2 of 1 indicates more confidence that the estimated data will actually represent the real data.

An R2 of 0 indicates no fit at all.

Except for Bozoisky, the R2 values for each grass are considered good to exceptionally good.

Hay Yields With and Without Nitrogen

Estimated hay yields with no applied nitrogen were lowest for Paiute orchardgrass followed by Manchar smooth bromegrass and highest for NewHy hybrid wheatgrass and Oahe intermediate wheatgrass.

Although NewHy and Oahe had similar estimated hay yields with no applied nitrogen, Oahe yielded an average of nearly twice as much additional hay per pound of applied nitrogen as NewHy.

As the amount of applied nitrogen increased, nitrogen use efficiencies declined in all the grasses.

With up to 100 pounds of applied nitrogen, Hycrest crested wheatgrass, Oahe intermediate wheatgrass, Manchar smooth bromegrass, and Luna pubescent wheatgrass appeared to be the most efficient in converting applied nitrogen to plant growth but thereafter the efficiency of Hycrest substantially dropped off to the point that applying more than 150 pounds per acre of nitrogen would not increase potential yield.

NewHy hybrid wheatgrass and Bozoisky Russian wildrye appeared to be least efficient in use of applied nitrogen for growth followed by Paiute orchardgrass and then Paddock meadow bromegrass.

Based on these low nitrogen use efficiencies, especially for NewHy and Bozoisky, selecting these grasses for irrigated hay field production, at least in northeast Wyoming, may be ill-advised.

Oahe Appears Top Producer

Estimated hay yields of Oahe intermediate wheatgrass were highest regardless of the amount of applied nitrogen.

This was apparently a result of the amount of growth produced without applied nitrogen in conjunction with its efficiency in converting applied nitrogen to plant biomass.

Both Manchar smooth bromegrass and Luna pubescent wheat- grass had similar nitrogen use efficiencies as Oahe, but because their estimated hay yields with no applied nitrogen averaged a half-ton per acre less than Oahe, this difference persisted with applied nitrogen.

The results of this two-year study indicate that Oahe intermediate wheatgrass may be the grass to select for hay production in northeast Wyoming irrigated fields.

Smooth bromegrass is the most common grass found in irrigated hay fields throughout Wyoming — most likely the variety Manchar — and, based on its nitrogen use efficiency as determined from this research project, it has not necessarily been a bad selection. However, based on our study, Manchar underperforms relative to Oahe intermediate wheatgrass at all nitrogen levels.

Other hay trial studies in Johnson and Sheridan counties have shown that smooth and meadow bromes generally yielded slightly more hay compared to intermediate and pubescent wheatgrasses regardless of whether fertilized with nitrogen or not. These contradictory findings show the need for additional research to provide a more definitive answer to the question of which perennial cool-season forage grasses are the most productive with the least amount of nitrogen fertilizer or in mixed stands with legumes such as alfalfa. ❖

This article appeared in most recent edition of the University of Wyoming College of Agriculture and Natural Science’s magazine, Reflections, published annually by the Agricultural Experiment Station. To see the entire issue, go to http://www.uwyo.edu/uwexpstn/publications/reflections/.